Starting on March 24th, I started receiving spam of this warning in my game in both the client log and the server log:
EndEffector (Part) must be descendant of ChainRoot (Part2).
IKControls are enabled and are used on characters for head movement. I have not changed anything about how they are set up, but started to receive this warning today. The EndEffector and ChainRoot are both siblings to each other and descendants to the same model.